SPINAL-CORD COORDINATION OF HINDLIMB MOVEMENTS IN THE TURTLE - INTERLIMB TEMPORAL RELATIONSHIPS DURING BILATERAL SCRATCHING AND SWIMMING

Hindlimb interlimb coordination was examined in turtles during symmetr ical ''same-form'' behaviors in which both hindlimbs utilized the same movement strategy (''form'') and during asymmetric ''mixed-form'' beh aviors in which the form. exhibited by one hindlimb differed from that of its contralateral partner. In spinal turtles, three forms of scrat ching were examined: rostral, pocket, and caudal. Bilateral symmetrica l same-form scratching was studied for each of the forms. Asymmetric m ixed-form scratching (rostral scratching of a hindlimb and pocket scra tching of the other hindlimb) was also examined. In intact turtles, tw o forms of swimming were examined: forward swimming and back-paddling. The symmetrical behavior of bilateral forward same-form swimming and the asymmetric behavior of turning mixed-form swimming (forward swimmi ng of 1 hindlimb and back-paddling of the other hindlimb) were studied . For all behaviors examined, most episodes displayed absolute or 1:1 coordination; in this type of coordination, during each movement cycle that began and ended with the onset of ipsilateral hip flexion, there was a single onset of contralateral hip flexion. For most of these ep isodes there was out-of-phase coordination between hip movements; the onset of contralateral hip flexion occurred near the onset of ipsilate ral hip extension midway through the ipsilateral movement cycle. Bilat eral caudal/caudal same-form scratching displayed out-of-phase 1:1 coo rdination during some episodes and in-phase 1:1 coordination during ot her episodes. During in-phase coordination, the onset of contralateral hip flexion occurred near the onset of ipsilateral hip flexion close to the start of the ipsilateral movement cycle. In a few cases of bila teral same-form scratching there were episodes of relative or 2:1 coor dination; in this type of coordination, during each movement cycle of the slowly moving limb that began and ended with ipsilateral hip flexi on, there were two distinct occurrences of the onset of contralateral hip flexion. The observation that out-of-phase movements of the hip oc curred during symmetrical as well as asymmetric behaviors is consisten t with the hypothesis that timing signals related to hip movement play a major role in interlimb phase control. The neural mechanisms respon sible for interlimb phase control ate not well understood in vertebrat es. The present demonstration of bilateral scratching in spinal turtle s suggests that this preparation may be suitable for additional experi ments to examine mechanisms of vertebrate interlimb phase control.